1. Field of the Disclosure
This disclosure relates generally to oxygen storage materials having high oxygen storage capacity with different applications and, more particularly, to the effect of aging in the phase stability of OSM which is free of platinum group metals and rare earth metals, for catalyst systems.
2. Background Information
Three-way catalysts (TWC), including platinum group metals (PGM) as active sites, alumina-based supports with a large specific surface, and, metal oxide promoter materials that regulate oxygen storage properties, are placed in the exhaust gas line of internal combustion engines for the control of carbon monoxide (CO), unburnt hydrocarbons (HC) and nitrogen oxides (NOx) emissions.
Oxygen storage material (OSM) included in a TWC catalyst system is needed for storing excess oxygen in an oxidizing atmosphere and releasing it in a reducing atmosphere. Through oxygen storage and release, a safeguard is obtained against fluctuations in exhaust gas composition during engine operation, enabling the system to maintain a stoichiometric atmosphere in which NOx, CO and HC can be converted efficiently.
Ceria (CeO2) was the first material used as OSM in catalyst systems because of its effective oxygen storage capacity (OSC) properties. Subsequently, a CeO2—ZrO2 solid solution replaced ceria because of its improved OSC and thermal stability. Current TWCs are exposed to high operation temperatures due to the use of closed-loop coupled catalysts near the engine. Additionally, the TWC's demand for PGM and rare earth (RE) metals continues to increase due to their efficiency in removing pollutants from internal combustion engine exhausts, placing at the same time a strain on the supply of PGM and RE metals, which drives up their cost and the cost of catalysts applications.
Recent environmental concerns for a catalyst's high performance have increased the focus on the operation of a TWC at the end of its lifetime. Catalytic materials used in TWC applications have also changed, and the new materials have to be thermally stable under the fluctuating exhaust gas conditions. The attainment of the requirements regarding the techniques to monitor the degree of the catalyst's deterioration/deactivation demands highly active and thermally stable catalysts.
Therefore, it may be desirable to have OSMs, without PGM and RE metal components, that may allow the preparation of a new generation of oxygen storage materials with very high OSC and oxygen ion mobility. These are very important elements for the advancement of TWC technology to effect emission reduction across a range of temperature and operating conditions, while maintaining or even improving upon the thermal and chemical stability under normal operating conditions and up to the theoretical limit in real catalysts.